The particular product in accordance with the invention is an extract of certain plants with the particular purpose of enrichment for phyto-oestrogens, both in their natural state and their closely related derivatives and metabolites.
Plants which are used as foodstuffs or medicinal herbs contain a wide variety of chemicals which are assimilated into the body following ingestion. Some of these chemicals are important nutrients for man and animals (e.g. fats, carbohydrates, proteins, vitamins, minerals) while others have none, or little or no known nutritional value. The phyto-oestrogens hitherto have fallen into this latter category of no known nutritional value.
There are 3 principal classes of phyto-oestrogens, viz. isoflavones, lignans, and coumestans. The isoflavones are thought to have a broad range of biological functions in plants, although these are poorly understood. However, two particular functions are recognised—(a) as phyto-alexin or stressor chemicals which are secreted by the plant in response to attack by parasites such as insects, fungi, viruses, etc and which display activity against these parasites, and (b) chemicals which encourage colonisation of nitrogen-fixing bacteria on the roots of legumes. The biological functions in plants of the lignans and coumestans is not generally understood.
The different types of phyto-oestrogens are as follows.
Type 1 Phyto-oestrogens—(Isoflavones)
Isoflavones appear to be widely distributed in the plant kingdom and over 700 different isoflavones are described. However, the isoflavones which display oestrogenic activity belong to a small sub-group and are restricted almost exclusively to the Leguminosae family. The known oestrogenic isoflavones are daidzein, formononetin, genistein and biochanin A. In common human foodstuffs such as soya, chickpeas, lentils and beans, the total levels of the oestrogenic isoflavones range between about 40 and 300 mg per 100 g dry weight.
In the raw plant material, isoflavones occur principally as glycosides. Following ingestion by man and animals, the glycoside moiety is hydrolysed free by a combination of gastric acid hydrolysis and fermentation by intestinal bacteria. Some of the isoflavones in the aglucone form are absorbed directly and circulate in the blood, while the remainder are metabolised by intestinal fermentation to a variety of compounds which are also absorbed. The absorbed isoflavones and their metabolites appear to undergo little or no further metabolism in the body, being readily transported in the bloodstream, and ultimately being excreted in the urine.
Type 2 Phyto-oestrogens (Lignans).
Lignans are widely distributed in the plant kingdom. Over one hundred lignans are described and they are reported in common human foodstuffs such as cereals, fruits and vegetables. Oilseeds such as flax (linseed) have the highest known levels at 20-60 mg/100 g dry weight, while cereals and legumes have much lower levels at 0.3-0.6 mg/100 g, and vegetables even lower levels at 0.1-0.2 mg/100 g. The most common lignan described is metairesinol. Dietary lignans also appear to be metabolised fairly efficiently within the gut by bacterial fermentation, yielding metabolites such as enterodiol and enterolactone which are absorbed into the bloodstream and excreted in the urine.
Type 3 Phyto-oestrogens (Coumestans).
Compared to isoflavones and lignans, oestrogenic coumestans appear to have a relatively restricted distribution in plants and generally occur at much lower levels. Alfalfa, ladino clover and some other fodder crops such as barrel medic may have significant levels and have been reported to cause reproductive dysfunction in grazing animals. In the human diet, the important sources of coumestans are sprouts of soya and alfalfa where levels up to 7 mg/100 g dry weight are reported. Whole soyabeans and other common foodstuff legumes contain levels of approx. 0.12 mg/100 g dry weight and most of that is concentrated in the seed hull which commonly is removed in the preparation of human foodstuffs.
Type 4 Phyto-oestrogens (Oestrogens).
These are compounds closely related to animal oestrogens such as oestrone. oestradiol and oestriol. These have been described in plants such as liquorice, apple, French bean, pomegranate and date palm. Little is known of the metabolism and biological significance of these chemicals in humans and animals.
The full range of biological effects in animals of these dietary phyto-oestrogens has received only recent study. A primary effect appears to be associated with their close structural relationship to naturally-occurring oestrogens which allows the phyto-oestrogens to mimic the effects of the endogenous oestrogens. The known biological effects of phyto-oestrogens can be summarised thus:
In vitro(a)bind to both cytoplasmic and nuclear membrane (Type II)oestrogen receptors on human tissues;(b)strongly compete with oestrogens for oestrogen receptors,but only weakly stimulate those receptors;(c)strongly stimulate the production of sex hormone-bindingglobulin (SHBG) from human cells;In vivo(d)weakly oestrogenic in animals;(e)competitively-inhibit the response of tissue to oestrogens.
The three major types of phyto-oestrogens appear to act at the cellular level in a similar manner, that is through interaction with cell surface oestrogen receptors. In the body, naturally-occurring oestrogens circulating in the blood largely exert their activity by interaction with oestrogen receptors on cell surfaces; such interactions then triggering a particular biological function of that particular cell. Phyto-oestrogens are able to bind to those oestrogen receptors because the structure of these compounds so closely resembles the endogenous oestrogens, but unlike the animal oestrogens, phyto-oestrogens only weakly activate the oestrogen receptor.
As a result of phyto-oestrogens and endogenous oestrogens competing for the oestrogen-binding sites on cells, the more weakly oestrogenic phyto-oestrogens can be considered to have an anti-oestrogenic effect. This phenomenon is known as competitive-inhibition, by which is meant that the biological effect of an active substance is impaired by the competitive binding to a target receptor of a similar but less active compound.
Thus a primary biological effect of phyto-oestrogens is held to be competitive inhibition of endogenous oestrogens. However, another more direct effect is the stimulation of synthesis of SHBG in the liver, as occurs with orally administered synthetic steroidal oestrogens. High levels of dietary phyto-oestrogens are thought to be responsible for the higher SHBG levels seen in vegetarians and in cultures maintaining traditional (high legume-containing) diets.
At high levels, dietary phyto-oestrogens can have profound physiological effects. An example of this is sheep and cattle grazing pastures containing a high proportion of subterranean clover or red clover which can contain levels of phyto-oestrogens as high as 5% of the dry weight of the plant. As a result of the competitively-inhibitory effect of the dietary phyto-oestrogens on endogenous oestrogen function in the hypothalamus, male and female sheep and cows can develop androgenic symptoms.
Such high dietary levels of phyto-oestrogens, however, are rare. It is far more common that most animal and human diets contain low to moderate levels of phyto-oestrogens, and there is growing epidemiological evidence that such levels have a beneficial effect on human health.
In most traditional human diets in developing countries, the principal phyto-oestrogens consumed are isoflavones because of the generally high reliance on legumes (also known as pulses) as a source of protein. The general consumption rates (g/day/person) for legumes for different regions currently are approximately: Japan (50-90), India (40-80), South America (30-70), North Africa (40-50), Central/Southem Africa (20-50) and Southern Mediterranean (30-60). Legumes also are a source of lignans and, to a much lesser extent, coumestans, and the additional cereal and vegetables in the diet would also boost the lignan intake. However, the isoflavone intake in these traditional cultures with high legume consumption would typically be much in excess of either lignan or coumestan intake.
The major types of legumes used in traditional diets include soya, chickpeas, lentils, ground nuts, beans (e.g. broad, haricot, kidney, lima, navy), and grams (bengal, horse and green).
In Western, developed countries, the daily intake of dietary phyto-oestrogens generally is negligible to low. In Western Europe, North America and Australasia, legumes were a major source of protein for the majority of the populations up to the end of the 19th century. From that time, legume consumption has declined significantly, being replaced in the diet with protein of animal origin. Average legume consumption in these regions currently is between 5-15 g/day/person with a significant proportion of the population ingesting little to no legumes or other phyto-oestrogen containing foods on a regular basis. Moreover, the types of legumes consumed in these regions (e.g. garden peas, French beans) have a typically lower isoflavone content than legumes such as soya and chick peas.
Based on typical consumption rates and types of foodstuffs consumed, the typical phyto-oestrogen intake (mg/day) for different regions can be calculated approximately as
IsoflavonesLignansCoumestansJapan50-3002-50.5Australia2-251-50.2
Thus it can be seen that regions which have maintained traditional diets have a higher average daily intake of phyto-oestrogens, particularly isoflavones, compared to western countries. People in communities such as Japan or developing countries with high legume intake excrete substantially higher phyto-oestrogen metabolites in their urine compared to people in Western countries. Within the latter, vegetarians also excrete higher phyto-oestrogen metabolite levels than do those consuming a more typical, omnivorous Western diet.
The presence of relatively large amounts of phyto-oestrogen metabolites in urine serves to highlight their potential biological significance. It has been shown that total urinary excretion of isoflavones and their active metabolites in people consuming moderate amounts of legumes is greatly in excess (up to 10,000×) of steroidal oestrogen levels. So that while the oestrogenicity of isoflavones to oestrogen receptors is only about 1% that of endogenous oestrogens, this weaker effect is off-set by the much higher blood levels of the isoflavones.
It is known that legumes have formed an important part of the human diet over the past 20,000-30,000 years. It therefore follows that human metabolism has evolved over at least this period in the presence of relatively large levels of dietary phyto-oestrogens particularly isoflavones. Given the known biological effects of phyto-oestrogens, it also follows that endogenous oestrogen metabolism and function has evolved in the face of significant competitive inhibiting effects of phyto-oestrogens. It has been speculated that the presence of significant dietary levels of phyto-oestrogens in recent human evolution has led to a degree of adaption by tissues responsive to reproductive hormones to these dietary components. That is, both the rate of production and/or the function of endogenous oestrogens may be either dependent upon or influenced by the presence of phyto-oestrogens in the body. It follows therefore that a relative deficiency of dietary phyto-oestrogens could be expected to lead to an imbalance of endogenous oestrogen metabolism.
There is increasing interest in the likely contribution of a relative deficiency of dietary phyto-oestrogens to the development of the so-called “Western diseases”, especially cancer of the breast, benign (cystic) breast disease, cancer of the uterus, cancer of the prostate, cancer of the bowel, pre-menstrual syndrome, menopausal syndrome, and atherosclerosis. All of these diseases are associated to a greater or lesser extent to oestrogen metabolism, and oestrogen function is either known or is suspected to play a role in their aetiology and/or pathogenesis.
Each of these diseases occurs at much higher incidence in Western, developed countries than it does in developing communities. Moreover, it is thought that in Western communities, the incidences of each have risen over the past century. It is also generally held, that of all the environmental factors likely to be contributing to this phenomenon, diet is the principal factor. Of those dietary components with the potential to influence the aetiology of oestrogen-related disease, there is a growing awareness that phyto-oestrogens may have important potential.
The beneficial effects of phyto-oestrogens on human health are thought to derive from at least two principal function, those being (i) competitive-inhibition of the function of endogenous oestrogens, and (ii) the stimulation of production of SHBG. SHBG plays an important role in primates in binding and transporting the reproductive hormones (oestrogens, androgens) in blood so that the availability of reproductive hormones is regulated to a large degree by SHBG levels. Higher SHBG levels are considered beneficial in leading to a reduction in both blood levels of unbound (and unregulated) reproductive hormones and metabolic clearance rates of the hormones. Although isoflavones are potent stimulators of SHBG synthesis, they only weakly bind to SHBG, so that the increased SHBG levels resulting from the dietary isoflavones are largely available for binding to endogenous oestrogens.
In terms of directly identifying the beneficial effects of phyto-oestrogens in amelioration of any or all of the “Western diseases”, there are only two examples. In one example, the diets of women, with menopausal syndrome were supplemented with foodstuffs (soya, linseed, red clover) high in phyto-oestrogens, and an alleviation of menopausal symptoms to an extent similar to that obtained with replacement therapy with synthetic oestrogens was achieved; that effect was ascribed to the phyto-oestrogen content of the supplement. In the other example, legumes such as soya and various pulses have been shown to have a hypocholesterolaemic effect in humans; this effect has not been ascribed to phyto-oestrogens, although purified (isoflavones do have a hypocholesterolaemic effect in animals with artificially-induced hypercholesterolaemia.
In summary, it could reasonably be deduced that the inclusion of greater levels of foodstuffs high in phyto-oestrogens in the standard diets of men and women in developed countries could be expected to redress a general imbalance of endogenous reproductive hormone metabolism, thereby reducing the predisposition of those communities to the above diseases. While there are various types of phyto-oestrogens which may be suitable to this end, the large discrepancy in isoflavone consumption between communities with Western and traditional diets suggest that foodstuffs with high isoflavone content are of prime interest.
However it is unrealistic to expect that public education programmes would readily convert communities in developed countries from a diet where the protein content is predominantly animal-derived, to one where the protein is predominantly legume-derived. Moreover, the legumes which are commonly consumed in developed countries are relatively poor sources of phyto-oestrogens and the general acceptance in the community of less well-known legumes with higher phyto-oestrogen content would be necessarily a slow process. Also, the highly variable levels of phyto-oestrogens in foodstuffs relating to plant strain type, degree of plant maturity, and climatic and other environmental conditions suggests that the supply of an assured amount of phyto-oestrogens through the use of whole foodstuffs may be difficult.
An alternative strategy is to make available either (i) phyto-oestrogens in a purified form, or (ii) foodstuffs which are enriched for phyto-oestrogens. In this way, the phyto-oestrogen could be added to the diet in a convenient form as a supplement without requiring any substantive change to the diet.